To enhance the effectiveness of radiation treatment of cancerous lesions, an improved in-vivo radiation monitoring sensor is required to quantify the dose rate and the absorbed dose. Modern treatment methods focus on concentrating the output from radioactive sources onto the cancer itself to minimize total body radiation exposure. Thus, real-time monitoring of radiation dose and dose rate can be used to optimize the radiation treatment. Conventional in-vivo radiation methods are able to measure the absorbed dose, but not the dose rate. In addition, they are influenced by environmental factors, such as the temperature and directionality of the source, and require physical access. The proposed in-vivo radiation monitor is based on a low-cost, scintillating, optical fiber probe that monitors in real-time the in-vivo dose rate and the absorbed dose of radiation. The probe is cylindrical in nature and its response is not influenced by the directionality of the source. Another unique feature to the proposed radiation sensor is that it does not require an external light source or electrical connection to probe the state of the sensor, thus making the sensor completely passive. PROPOSED COMMERCIAL APPLICATIONS: The proposed in-vivo radiation monitor has the potential to provide the medical community with a low cost radiation sensor that can monitor the dose rate and absorbed dose to which tissues are exposed during internal and external irradiation. This device will enable physicians to deliver the correct dose of radiation to eliminate cancerous tumors, thus increasing the effectiveness of radiation treatments and reducing overall treatment costs.